Miniature jacks of the type disclosed in U.S. Pat. No. 3,850,497 issued to C. L. Krumreich, A. E. Mulbarger, Jr., and S. W. Walden on Nov. 26, 1974, are now coming into common use in the telephone industry for providing connections to one or more telephone lines, each line consisting of two conductors conventionally referred to as tip and ring. The jacks accommodate miniature plugs of the type disclosed in U.S. Pat. No. 3,761,869 issued to E. C. Hardesty, C. L. Krumreich, A. E. Mulbarger, Jr., and S. W. Walden on Sept. 25, 1973, which plugs are used to terminate station equipment such as telephone sets. In addition, the jacks are wired in parallel with the associated telephone lines, and this provides all station equipment connected to jacks wired to the same telephone line equal access to that line.
However, with some station equipment, such as automatic reporting telephones used in security systems, it is necessary for the telephone to be always able to seize the telephone line when an alarm condition occurs. Of course this can be accomplished by having just the alarm reporting telephone connected to a telephone line, but it is costly to dedicate a telephone line to this one use. A more practical solution is to connect the reporting telephone in series with the telephone line ahead of all other station equipment connected to that line. The reporting telephone is then designed to provide continuity to the telephone line, and it is able to disconnect the other station equipment when an alarm condition occurs. It is therefore assured of access to the telephone line at all times.
Since the previously referred to miniature jack has at least four contacts, it is certainly possible to connect it in series with a telephone line for use with such series station equipment. However, should the series station equipment be unplugged from such a series-wired jack, continuity in the telephone line would be broken and all other station equipment connected to the line would be disabled. Since it would not be obvious that the jack is wired differently, such inadvertent disruption of service would likely occur. Furthermore, inasmuch as the miniature plugs and jacks are being introduced to permit the installation and removal of station equipment by the subscribers themselves, it is undesirable to create a situation that requires a telephone installer to rewire a jack when the station equipment connected thereto is changed.